The present invention relates to co-initiated polyether polyols useful for the production of rigid polyurethane foams and to a process for the production of such co-initiated polyols.
Processes for the production of polyether polyols from materials which are normally solid at ambient conditions such as sucrose are known. In many of the known processes, the solid material is dissolved or suspended in a solvent prior to reaction with the selected alkylene oxide(s) to facilitate processing of the reaction mixture. The solvent can either be an inert material such that disclosed in U.S. Pat. No. 3,941,769 or a reactive material such as water (U.S. Pat. No. 5,596,059).
The presence of water or an inert organic solvent during the reaction of the solid material with the alkylene oxide, however, is undesirable for a number of reasons. First, the solvent takes up space in the reactor which might otherwise be used to produce larger batches of polyol. Second, the solvent or unreacted water must be removed, usually by distillation. Such removal consumes both time and energy. Finally, if water is used to suspend or dissolve the sucrose, difunctional glycols which reduce the average functionality of the polyol produced are formed. One proposed solution to this problem is removal of the solvent by distillation after a portion of the alkylene oxide has been added. (See, e.g., U.S. Pat. No. 3,085,085 which discloses removal of water by distillation.) Such removal of water after adding and reacting a portion of the total alkylene oxide desired reduces the amount of glycols formed and allows for a larger batch size but still consumes time and energy.
In commercial processes for the production of polyurethane foams, mixtures or blends of individual polyols are generally used as the polyol component to be reacted with the isocyanate component. Use of such mixtures makes it possible to produce polymers having specific physical properties suited for a particular application.
When developing new systems, combination of individual polyols makes it easier to optimize a system for the production of polymers having a desired combination of properties. However, once a system has been optimized, the flexibility achieved by use of individual polyols is no longer necessary. This is particularly true where one or more of the polyols in the optimized system is difficult to manufacture such as polyols based on solid initiators such as sucrose. In such cases, it may be desirable to produce a co-initiated polyol which duplicates the properties obtained from the blend of individual polyols.
In U.S. Pat. No. 5,684,057, for example, a polyol composition to produce a rigid foam having improved thermal insulation and dimensional stability when specified blowing agents were used was sought. The polyol composition developed includes at least three different types of polyol. The polyol composition required in this patented process includes: (1) an aromatic amine-initiated polyether polyol, (2) an aliphatic amine-initiated polyether polyol, and (3) a polyester polyol. This patent teaches that the individual polyols may be combined prior to reaction with the polyisocyanate. It is preferred, however, that the aromatic amine-initiated and aliphatic amine-initiated polyols be prepared by a co-initiation process in which the aliphatic and aromatic amine initiators are first blended together and the resultant blend is subsequently alkoxylated. The required polyester polyol is then added to the propoxylated blend.
U.S. Pat. No. 5,596,059 discloses polyol blends for the production of flexible foams which do not require the use of expensive initiators such as glycerine or of solvents such as toluene. These polyol blends are prepared by alkoxylating aqueous solutions of one or more solid, polyhydric, hydroxy-functional initiators to produce a blend of low functionality diols and higher functionality polyols. A key feature of this process, is the alkoxylation of the water used as solvent. This alkoxylation of water eliminates the need for water removal and the need to use expensive conventional initiators such as glycerine or solvents. Water co-initiated polyols such as these, however, are not useful for the production of rigid polyurethane foams because of their low functionalities and hydroxyl numbers.
A polyol blend for the production of rigid polyurethane foams which could be prepared from a solid polyhydroxyl compound initiator by a simple process without the need to use a solvent would, therefore, be advantageous.
It is an object of the present invention to provide a process for the production of a co-initiated polyether polyol from a polyhydroxyl compound that is normally solid at processing conditions without the need to use large quantities of a solvent that must be removed prior to use of that co-initiated polyol and without generating large amounts of low functionality diols.
It is also an object of the present invention to provide a more efficient and economical process for the production of a co-initiated polyether polyol having a functionality of at least 4 from a polyhydroxyl compound that is normally solid at processing conditions.
It is a further object of the present invention to provide a co-initiated polyol for the production of rigid polyurethane foams which produces foams having properties comparable to foams made with polyols formed by the conventional method for producing blends, i.e., combining individual polyols.
These and other objects which will be apparent to those skilled in the art are accomplished by suspending a solid polyhydroxyl initiator having a functionality of at least 4 and a melting or decomposition point above 95xc2x0 C. in an amine-initiated polyol, heating the suspension, (preferably, in the presence of an alkaline catalyst) and alkoxylating the resultant mixture. The alkaline catalyst may then be neutralized and/or removed from the alkoxylated mixture. The alkoxylation product may then be used in a process for the production of rigid polyurethane foams.
The present invention relates to a new method for producing co-initiated polyether polyols from polyhydroxyl compounds that are solids at ambient temperature without the use of an inert solvent such as toluene or the large quantities of water necessary to suspend or dissolve the solid polyhydroxy compound. In this method, at least one solid polyhydroxyl compound is suspended in at least one amine-initiated polyol, the suspension is heated to or maintained at a temperature of at least 80xc2x0 C. in the presence of an alkaline catalyst and subsequently alkoxylated. The alkaline catalyst is then neutralized and/or removed from the alkoxylated mixture by any of the known techniques such as neutralization with sulfuric acid or lactic acid, extraction or decantation. The resultant alkoxylated mixture may then be used to prepare rigid polyurethane foams.
The solid polyhydroxyl compounds useful as the initiator to be suspended in the amine-initiated polyol have a hydroxyl group functionality of at least 4 and melt at temperatures above 95xc2x0 C. or decompose before melting. Examples of suitable polyhydroxyl compound initiators include: pentaerythritol, dipentaerythritol, glucose, sorbitol, lactose, mannitol, fructose, sucrose, hydrolyzed starches, saccharide and polysaccharide derivatives such as alpha-methylglucoside and alpha-hydroxyethyl-glucoside. Sorbitol, sucrose, and pentaerythritol are particularly preferred.
The amine-initiated polyol in which the solid polyhydroxyl compound is suspended may be any of the known amine-initiated polyether polyols which is liquid at temperatures of from about 70 to about 150xc2x0 C., has a viscosity at the processing temperature which is sufficiently low that it will form a suspension that can be stirred, and has a hydroxyl number sufficiently high that upon alkoxylation the co-initiated polyether polyol product will have the predetermined hydroxyl number of greater than 300 mg KOH/g. The hydroxyl number of the amine-initiated polyols will generally be at least 500, preferably at least 550, most preferably at least 600 mg KOH/g. The hydroxyl numbers given herein are determined in accordance with ASTM D-2849-69, Method C.
Examples of suitable amines that may be used to prepare the amine-initiated polyether polyols satisfying these criteria include: 2,4xe2x80x2-, 2,2xe2x80x2-, and 4,4xe2x80x2-methylene dianiline; 2,6- or 2,4-toluene diamine and vicinal toluene diamines; p-aminoaniline; 1,5-diaminonaphthalene; mixtures of methylene dianiline and its higher homologs; ethylene diamine, propylene diamine; diethylene triamine; 1,3-diaminopropane; 1,3-diaminobutane; and 1,4-diaminobutane. Ethylene diamine and toluene diamines are particularly preferred. Ammonia and aminoalcohols which can be prepared by the alkoxylation of ammonia are not included among the amine-initiators to be used in the amine-initiated polyols required for the practice of the present invention.
The amine-initiated polyols may be produced by any of the known methods. Generally, such polyols are produced by alkoxylating the amine initiator, either with or without an alkaline catalyst, until the desired hydroxyl number has been attained.
Suitable alkoxylating agents include any of the known alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, and mixtures thereof. Ethylene oxide and propylene oxide are preferred.
In accordance with the present invention, the solid polyhydroxyl compound initiator is added to the liquid amine-initiated polyol and stirred, mixed or agitated sufficiently to disperse the polyhydroxyl compound initiator in the amine-initiated polyol and form a solution or a suspension. The amine-initiated polyol is generally used in an amount that is at least 30% by weight (based on the weight of the solid polyhydroxyl compound), preferably at least 40% by weight, most preferably, at least 50% by weight.
The addition of solid polyhydroxyl compound to the amine-initiated polyol is generally carried out at a temperature less than 120xc2x0, preferably from about 70 to about 110xc2x0 C., most preferably from about 80 to about 100xc2x0 C.
In addition to the solid polyhydroxyl compound, other starting materials commonly used in the production of polyether polyols and any of the catalysts commonly used to produce polyether polyols may, optionally, also be included in the suspension. Examples of other starting materials that may optionally be included in the suspension are small quantities of water, ethylene glycol, propylene glycol and glycerine. As used herein, xe2x80x9csmall quantities of waterxe2x80x9d means less than about 10% by weight, based on the weight of the solid polyhydroxyl compound initiator, including water added with any aqueous catalyst solution. The total quantity of these other, optional, starting materials should not, however, be greater than 25% by weight, based on the weight of the solid polyhydroxyl compound initiator.
Examples of catalysts that may be included in the suspension include potassium hydroxide and sodium hydroxide. When sucrose is used as the solid polyhydroxyl compound initiator, an alkaline catalyst such a potassium hydroxide should be included in the solution or suspension.
After the suspension of the solid polyhydroxyl compound in the amine-initiated polyol has been formed, the suspension is adjusted to a temperature of from about 80 to about 150xc2x0 C., preferably from about 90 to about 140xc2x0 C., most preferably from about 100 to about 130xc2x0 C. This heated suspension is then alkoxylated in accordance with any of the procedures known to those skilled in the art using an alkylene oxide such as ethylene oxide and/or propylene oxide at a temperature of from about 80 to about 150xc2x0 C., preferably from about 90 to about 140xc2x0 C., most preferably from about 100 to about 130xc2x0 C. This alkoxylation is carried out until the desired hydroxyl number is attained. The co-initiated polyol of the present invention will generally have a hydroxyl number of from about 300 to about 600, preferably from about 350 to about 550, most preferably from about 400 to about 500 mg KOH/g, and a number average functionality of from about 4 to about 6, preferably from about 4 to about 5.
However, it is also possible to produce a co-initiated polyether polyol having a lower or a higher hydroxyl number by simply increasing or decreasing the amount of alkoxylation agent added. It is also possible to produce a co-initiated polyether polyol having a higher or lower functionality by selecting an amine-initiated polyol having a different functionality or by varying the ratio of amine polyol to solid polyhydroxyl compound to any other starter material used.
A key feature of the present invention is the ability to produce a polyether polyol from a solid polyhydroxyl compound without the use of added solvent and without sacrificing any of the product properties. The absence of a solvent makes it possible to produce the desired co-initiated polyether polyol in greater quantity without increasing the volume of the reaction vessel. Further, the production cycle time is reduced because there is no need for the additional processing step of solvent removal. Finally, safety, health and environmental concerns encountered with use of solvents such as flammability, toxicity, and environmental releases are avoided.
After any alkaline catalyst present has been neutralized and/or removed, the co-initiated polyether polyols produced in accordance with the present invention may be used for the production of rigid polyurethane foams in accordance with known methods. These co-initiated polyether polyols may be used alone or in combination with other polyols.
Other polyols which may optionally be used in combination with the co-initiated polyether polyols of the present invention include polyether polyols prepared from liquid polyhydroxyl compounds, polyether polyols prepared from polyhydroxyl compounds having functionalities of less than 4, polyether polyols prepared from ammonia or aminoalcohols, polyester polyols and combinations thereof.
The additives and processing aids typically included in the polyol component of a foam-forming mixture may, of course, be added to the co-initiated polyether polyols of the present invention prior to use of the co-initiated polyether polyol to produce a rigid polyurethane foam. Examples of such suitable additives and processing aids include: catalysts, blowing agents, water, chain extenders, crosslinking agents, surfactants, foam stabilizers, cell regulators, fillers, dyes, pigments, flame retardants, hydrolysis protection agents, fungicides and bacteriocides.
Suitable catalysts include organometallic, preferably organotin catalysts, and tertiary amine catalysts. Examples of suitable tin catalysts are tin (II) acetate, tin (II) octanoate, tin (II) laurate, dialkyl tin diacetates, and dibutyl tin dichloride. Examples of suitable tertiary amine catalysts include: N,N-dimethyl cyclohexyl amine, pentamethyl diethylene triamine, and N, Nxe2x80x2, Nxe2x80x3-tris(3-dimethyl aminopropyl)hexahydro-S-triazine. Tertiary amines are the preferred catalysts.
Suitable blowing agents include any of those known in the art used singly or in combination. Hydrocarbons, hydrofluorocarbons (HFCs), and hydrochlorofluorocarbons (HCFCs) and carbon dioxide generated from the reaction of water with an isocyanate are particularly suitable. Specific examples of suitable blowing agents are: 1,1-dichloro-1-fluoroethane (HCFC 141b), 1,1,1,2-tetrafluoro-ethane (HFC 134a), chlorodifluoromethane (HCFC 22), 1-chloro-1,1-difluoroethane (HCFC 142b), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC 124), 1,1,2,2-tetrafluoroethane (HFC 134), 1,1,1,3,3-pentafluoropropane (HFC 245fa), 1,1,1,3,3-pentafluorobutane (HFC 365mfc), 1,1,1,4,4,4-hexafluorobutane (HFC 356mffm), cyclopentane, isopentane, cyclo-hexane, and isobutane. Hydrocarbons and HFC""s are the most preferred blowing agents because they have a zero ozone depletion potential.
The isocyanates which may be reacted with the co-initiated polyols of the present invention include any of the known aliphatic isocyanates, aromatic isocyanates, modified isocyanates, and isocyanate-terminated prepolymers. The isocyanate will generally have at least two isocyanate groups, preferably from 2 to 3 isocyanate groups per molecule. Examples of suitable isocyanates are: toluene diisocyanate (TDI), prepolymers of toluene diisocyanate, methylene diphenyl diisocyanate (MDI), prepolymers of methylene diphenyl diisocyanate, polymeric methylene diphenyl diisocyanate (PMDI), and prepolymers of polymeric methylene diphenyl diisocyanate.
The isocyanate and the isocyanate-reactive component in which the co-initiated polyols of the present invention are present are generally reacted in amounts such the ratio of NCO to OH groups is from about 0.9 to about 3.0, preferably from about 1.0 to about 2.0, most preferably from about 1.05 to about 1.5.
Polyurethane foams made from the co-initiated polyether polyols of the present invention are characterized by physical properties comparable to those of foams made using mixtures of individual polyether polyols having the same amine and the same polyhydroxyl compound initiators and the same average hydroxyl numbers despite their inherent structural differences.
Having thus described our invention, the following Examples are given as being illustrative thereof. All parts and percentages given in these Examples are parts by weight and percentages by weight, unless otherwise indicated.